Water as it evaporates into the atmosphere and condenses back to land and water represents the hydrologic cycle of our planet. It is water that weaves the earth to the sea and the skies. Salt, which is present mostly as table salt or sodium chloride in seawater, is actually molecules that break apart in water, forming ions, carrying positive or negative electrical charges. More ions, sulfate (SO42-), magnesium (Mg2+), calcium (Ca2+), potassium (K+) and bicarbonate (HCO3-), are also present in the sea but account for no more than about .02 percent of the sea’s salinity. So sodium chloride represents the bulk of dissolved solids in the sea, coming mostly from rivers as well as from hot fluids from hydrothermal vents deep on the ocean floor, and from volcanic gases. As we all know, all rivers drain to the sea, in fact depositing about three billion metric tons of salts to the ocean each year. So all the dissolvable solids from the earth, as soon as water passes over them as in rainfall or floods, will drain to the rivers, to the sea, then to the oceans. What is even more amazing is that despite the constant draining of the river salts to the oceans, the average ocean salinity has remained constant for at least over a billion years. Life processes have ensured this constancy. These include processes like the chemical bonding of salts to clay sediments, when marine organisms use salt to enhance their own body processes or even form body parts or when salts precipitate out of the sea to form minerals or into the air that makes for the "taste of the sea" when we breathe air on a nearby shore.
While the ocean’s salinity has remained constant, the salinity of seas, however, varies. Naturally, where heat is greatest, and evaporation more intense and rainfall is scarce, in the subtropical deserts, the salinity of seawater is highest, while in the reverse conditions in the temperate and sub-polar regions, salinities are lowest. The Red Sea is known to possess the highest salinity in the world with 320g/kg in temperatures of 58 degrees C (salinity of deep waters is at 34.6 to 34.9 g/kg throughout the world). In the wet tropical regions, salinity could be said to be on the average since evaporation and rainfall are more or less balanced in their presence.
Once again, the sea teaches us about substance and how it flows, carving in open minds the insight that everything lives, drains, evaporates and returns in some form or another. The planet is not ours. The sea does not belong to us as maps tell us; we are simply salt that moves with it.